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Biomedical subjects

R Larsen

Publications and source records attributed to R Larsen.

At least 145 records · Page 8Linked to original sources
PubMed1988

[The effects of isoflurane and enflurane on cerebral hemodynamics and cerebral oxygen consumption in humans].

The effects of isoflurane (1 MAC) and enflurane (1 MAC) on cerebral blood flow and cerebral oxygen consumption were studied in 20 male patients without intracranial disease undergoing coronary artery bypass surgery (mean age 57 and 59 years respectively). The aim of the study was to investigate whether both agents diminish autoregulation of cerebral blood flow and CO2 reactivity of cerebral blood vessels. Patients were randomly assigned to one of two groups (10 patients each) receiving either isoflurane 1.15 vol.% or enflurane 1.68 vol.% endexpiratory. Measurements were performed and blood samples were taken in the awake state (I); 15 min after achievement of steady-state conditions with 1.68 vol.% enflurane or 1.5 vol.% isoflurane without blood pressure support (II); during norepinephrine-induced hypertension at a cerebral perfusion pressure of 110 mmHg (III); and during controlled hyperventilation at a PaCO2 of 27 mmHg and normotension (IV). Cerebral blood flow was measured by the argon wash-in technique. Isoflurane and enflurane produced a significant drop in cardiac index and cerebral perfusion pressure and reduced cerebral blood flow significantly by 35% and 39% respectively. Cerebral oxygen consumption was also significantly decreased by 49% (isoflurane) and 50% (enflurane). Induced hypertension with norepinephrine increased cerebral blood flow significantly by 32% (isoflurane) and 26% (enflurane), while hypocapnia reduced cerebral blood flow significantly by 26% (isoflurane) and 29% (enflurane).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Global and regional myocardial blood flow and metabolism during equipotent halothane and isoflurane anesthesia in patients with coronary artery disease.

Global and regional myocardial blood flow and metabolism were examined in 20 patients with coronary artery disease before surgical stimulation. Half were anesthetized with halothane (0.8%) and half with isoflurane (1.2%). Coronary perfusion pressure decreased similarly in both groups. During halothane anesthesia coronary sinus blood flow, an index of global perfusion, decreased from an awake value of 129 +/- 7 to 97 +/- 7 ml/min (P less than 0.05), and great cardiac vein blood flow, an index of regional perfusion, decreased from 60 +/- 8 to 44 +/- 5 ml/min (P less than 0.05). In contrast, during isoflurane anesthesia global coronary blood flow increased from 131 +/- 13 to 153 +/- 16 ml/min (P less than 0.05), while regional blood flow decreased from 68 +/- 7 to 56 +/- 6 ml/min (P less than 0.05). Thus, the ratio of great cardiac vein blood flow to coronary sinus blood flow was unchanged during halothane anesthesia but decreased significantly during isoflurane. Neither global nor regional coronary vascular resistance was altered by halothane, whereas isoflurane decreased global coronary vascular resistance without affecting regional coronary vascular resistance. All patients receiving halothane had net myocardial lactate extraction. In the isoflurane group, four patients showed global lactate production and three regional lactate production. All patients demonstrating lactate production also developed electrocardiographic evidence of myocardial ischemia, which was not present before induction. The authors conclude that halothane is a preferable anesthetic to isoflurane in patients with coronary artery disease because the latter has the propensity to induce maldistribution of the coronary circulation and myocardial ischemia.

Adult↗
PubMed1987

Regulation of starch synthesis: enzymological and genetic studies.

Significant advances have been made with respect to elucidating the structure, the allosteric site, interactions of effectors, covalent modifications, and the amino acid sequence of the ADPG synthetase. It is hoped that in the near future, sufficient information will be obtained to enable facile manipulation of the plant tissue ADPG synthetase gene and its product.

Allosteric Site↗
PubMed1987

Effect of bile acids on hepatic protoporphyrin metabolism in perfused rat liver.

To determine the effect of bile acids on hepatic protoporphyrin metabolism, balance studies were performed in isolated perfused rat livers. Hepatic protoporphyrin metabolism was found to increase linearly as a function of protoporphyrin dose in livers infused with and without taurocholate (0.7 mumol/min), but their rates differed significantly. Employing a standard 1500-nmol protoporphyrin bolus dose, infusions (0.7 mumol/min) of taurocholate, glycocholate, deoxycholate, and chenodeoxycholate, but not tauroursodeoxycholate or ursodeoxycholate, increased protoporphyrin metabolism 1.7- to 2.7-fold over control (0 bile acid) values. Bile acid infusion ranging from 0.175 to 1.4 mumol/min confirmed that both taurocholate and chenodeoxycholate increased protoporphyrin disposal significantly more than ursodeoxycholate. For all bile acids, the increase of protoporphyrin metabolism was most pronounced between biliary bile acid excretion rates of 10-50 nmol/min.g liver. These data indicate that (a) bile acids facilitated protoporphyrin metabolism, (b) bile acid structure influenced the effect, and (c) ursodeoxycholate may not be a prime candidate to study the role of bile acids in the treatment of protoporphyria.

Animals↗
PubMed1987

Determination of depth for electron breast boosts.

A technique has been developed to determine the depth for the electron boost treatments for patients undergoing definitive irradiation for early stage breast cancer. A series of parallel link chains are placed on the breast over the clinically determined site of the boost. Using fluoroscopy, the physician confirms that the chains overlie the tumor bed which is outlined by radiopaque surgical clips placed at the time of the breast biopsy. A pair of orthogonal films and/or rotational stereo shift films are obtained with a standard simulator unit. Using the image of the chains to define the surface contour, the depth of each surgical clip is measured directly from the orthogonal films or calculated from the rotational stereo shift films. With this information, the physician can determine the appropriate electron energy to cover the target volume. This method was tested by comparison with depths measured from CT scan, and close agreement was demonstrated.

Breast Neoplasms↗
PubMed1987

Blinking patterns in soft contact lens wearers can be altered with training.

The blinking patterns of 15 soft contact lens wearers were recorded with a concealed video camera. Each of 20 consecutive blinks were graded, during slow motion replay of the video, as either complete, incomplete, forced, or twitch. Ten of these subjects were instructed to perform blinking exercises for a period of 2 weeks and the remaining 5 subjects acted as controls. After these exercises all the experimental group displayed an increased frequency of complete blinks, whereas the blinking patterns of the control group remained unchanged. Blinking exercises are likely to alleviate many of the signs and symptoms associated with incomplete blinking amongst contact lens wearers.

Blinking↗
PubMed1987

Incontinentia pigmenti: association with anterior horn cell degeneration.

Incontinentia pigmenti (IP) has been associated with CNS involvement, including seizures, retardation, motor abnormalities, and malformations in greater than 30% of patients. Motor symptoms include spasticity and hyperreflexia; however, weakness and flaccidity have also been described. Peripheral nervous system neuropathology in patients with IP has not previously been reported. The infant with IP in this report showed generalized weakness due to anterior horn cell degeneration. The neuropathologic findings in both the central and peripheral nervous systems will be reviewed and contrasted to previous reports. Patients with IP and weakness should undergo neurodiagnostic evaluation of peripheral nervous system function.

Anterior Horn Cells↗
PubMed1986

Spinal cord protection during radiation therapy.

Treating intrathoracic malignancies to high doses, particularly those of lung and esophagus, requires limiting the radiation dose delivered to the spinal cord. Several factors are important in determining the cord dose. These are: The distance from the block or collimator edge to the cord, the variation of dose with distance from the block or collimator edge and, the expected variation of this distance for clinical set-up from day-to-day. When treating with an oblique beam, the position of the cord may be difficult to identify. A technique for localizing the spinal cord on a simulator film at an arbitrary gantry angle is presented. The technique requires determination of distances from the central axis of the beam to the medial aspect of the pedicle and posterior vertebral body. These can readily be obtained from measurements on orthogonal, AP/PA and lateral isocentric simulator radiographs. A mathematical transformation is applied to determine the corresponding cord locations on the oblique radiographs for any arbitrary gantry angle. The accuracy of cord localization was within 2-3 mm with a precision of 2 mm for five physicians who used this technique. The beam edge characteristics for 60Co, 6 MV, and 10 MV teletherapy unit were measured for various depths and field sizes. For the 6 and 10 MV units, the beam penumbra is nearly independent of the field size, depth and field defining devices (inner and outer collimator jaws, trimmer bars, and shielding blocks). Because the beam penumbra is dependent on the design of the linear accelerator, its measurement should be made individually for each linear accelerator. Our preliminary data on patient positioning uncertainty did not exceed the 6-8 mm limit documented in the literature.

Humans↗
PubMed1986

[Coronary circulation, myocardial oxygen consumption and myocardial metabolism during enflurane-nitrous oxide anesthesia in coronary patients].

The effects of enflurane on myocardial oxygen consumption, metabolism and coronary blood flow (argon washin) were studied in 10 patients with 2- or 3-vessel coronary artery disease undergoing coronary artery bypass surgery. All patients were men with stable angina and normal left ventricular function and were on maintenance doses of beta-receptor- or calcium-antagonists. Anaesthesia consisted of enflurane and 50% nitrous oxide in oxygen. Measurements were performed and blood samples were taken with the patient awake, 30 min after induction of anaesthesia without any surgical stimulation and during sternotomy. End-tidal enflurane concentrations averaged 0.9% after induction and 2.5% during sternotomy. Enflurane decreased coronary blood flow significantly by 36% after induction, while sternotomy increased coronary blood flow by 29%. Myocardial oxygen uptake was decreased by 33% and was increased by 37% during sternotomy. Coronary vascular resistance did not change significantly during the entire observation period, while coronary sinus oxygen saturation significantly increased after induction by 20% followed by a decrease to preinduction levels during sternotomy. Myocardial glucose, free fatty acids, lactate and pyruvate uptake were significantly reduced after induction and increased to preinduction levels during sternotomy. Myocardial lactate production could not be demonstrated at any time during the observation period.

Anesthesia, Inhalation↗
PubMed1986

[Isoflurane: coronary blood flow and myocardial metabolism in patients with coronary heart disease].

The effects of isoflurane on myocardial oxygen uptake, metabolism and coronary blood flow (argon washin-technique) were studied in 10 patients undergoing three-vessel coronary artery bypass surgery. All patients were men with stable angina and normal left ventricular function and were receiving maintenance doses of beta-receptor antagonists or calcium channel blocking drugs. Anaesthesia consisted of isoflurane and 50% nitrous oxide in oxygen. Measurements were performed and blood samples were taken with the patients awake, 20 min after induction of anaesthesia without surgical stimulation, and during sternotomy and sternal spread. End-tidal isoflurane concentrations averaged 0.4% after induction of anaesthesia and 1.5% during sternotomy. Isoflurane significantly decreased myocardial blood flow by 18% following induction of anaesthesia, while sternotomy increased myocardial blood flow to pre-induction levels. Induction decreased myocardial oxygen uptake by 32%, while sternotomy increased oxygen uptake by 21% vs post-induction values. Myocardial uptake of glucose, lactate, free fatty acids and pyruvate significantly decreased after induction and increased to pre-induction levels during sternotomy. Myocardial lactate production, indicating myocardial ischaemia, was observed in 1 patient after induction and in three patients during sternotomy; three additional patients demonstrated a marked reduction in myocardial lactate uptake after induction and during sternotomy. It is concluded that all changes in myocardial metabolism, oxygen uptake and coronary blood flow were the result of a decrease in haemodynamic load on the myocardium and reduced contractility, while the increase in these parameters during sternotomy was due to an increase in myocardial work.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1986

The effect of spironolactone on the cardiocirculatory responses to upright tilt at sea level and at simulated high altitude.

The objective of this study was to determine if spironolactone (S) alters the cardiocirculatory responses to upright tilt at sea level (SL;50 m) and during 44 h of simulated altitude (HA;4,600 m). In a double-blind, crossover-designed study, 9 male subjects (age range: 18-25 years) received 25 mg orally, four times per day of either S or an identically-appearing placebo (P) 2 d prior to and during HA. The crossover was separated by 2 weeks. Heart rate, stroke volume, cardiac output, calf blood flow, total peripheral resistance and systemic blood pressure were obtained during supine rest and after 10 min of 60 degrees head-up tilt using an impedance monitor and an electro-sphygmomanometer. The 24-h determinations of urinary volume, sodium and potassium as well as venous plasma values for sodium, potassium and chloride were obtained daily. There were no statistically significant differences between P and S treatment periods for: caloric, electrolytes or fluid ingestion; urinary volume or electrolytes; plasma electrolytes; or any of the cardiocirculatory parameters measured in the supine or upright position at SL or during HA. It was concluded that S did not induce a significant diuresis or significantly alter vascular responsiveness to negatively effect the normal cardiocirculatory responses to upright tilt at sea level or simulated high altitude.

Adult↗
PubMed1985

[Cardiovascular effects of isoflurane-nitrous oxide anesthesia in peripheral and abdominal surgical interventions].

The cardiovascular actions of isoflurane-nitrous oxide anesthesia were studied in 20 patients (age rage 46-76 yr) undergoing laparatomy (group A = 13 patients) or peripheral vascular surgery (group B = 7 patients). Measurements were performed in the awake state, 20 min after induction of anesthesia and during surgical stimulation. Isoflurane produced small changes in heart rate but a significant reduction in mean arterial pressure which was due to a reduction in peripheral vascular resistance and myocardial contractility. During surgical stimulation arterial pressure rose above control values in group A but remained below control in group B. Cardiac index and stroke volume index both decreased after induction of anesthesia in group A and B. During surgical stimulation cardiac index increased in group A due to an increase in heart rate but remained below control in group B, while stroke volume index was reduced in both groups throughout the whole procedure. These results suggest, that contrary to the findings in human volunteers, isoflurane produces a significant cardiovascular depression in aged surgical patient.

Abdomen↗
PubMed1985

[The effect of rewarming of stored blood on plasma value and erythrocytes].

30 units of stored blood of different age were rewarmed from 4 degrees C to 32 degrees C by microwave blood-warmer Infusotherm 407. The resulting damage to blood components and change of function of erythrocytes were compared with those caused by storage of CPD-blood. Dependent on the age of stored blood we found considerable increases in the plasma-levels of potassium, lactate, and free haemoglobin. Compared with cold CPD-blood rewarming of stored blood produced a 7% increase in lactate and a 8% increase in free haemoglobin. There were no changes in platelet and erythrocyte counts, haematocrit, plasma-levels of haemoglobin, electrolytes, cholesterol, blood viscosity, osmotic resistance, and oxygen-binding capacity. As damage of stored blood produced by warming is minimal compared with that produced by storage, the Infusotherm 407 is considered to be a clinically useful blood-warmer.

Blood Cell Count↗
PubMed1983

Myocardial blood flow and oxygen consumption during halothane-nitrous oxide anaesthesia for coronary revascularization.

The effects of halothane on myocardial blood flow and myocardial oxygen balance were studied in seven male patients with stable angina and normal left ventricular function. Patients were receiving maintenance doses of beta-receptor antagonists and underwent coronary artery bypass surgery. Anaesthesia consisted of halothane and 50% nitrous oxide in oxygen. Halothane decreased myocardial blood flow and myocardial oxygen consumption by 29% and 32%, respectively, after induction of anaesthesia, and during sternotomy. Myocardial lactate production was not observed at any time. Cardiac index, stroke volume index, mean arterial pressure and mean diastolic arterial pressure were decreased significantly after induction of anaesthesia and during sternotomy. Heart rate remained unchanged. The global myocardial oxygen supply and demand relationship was maintained. The results suggest that halothane is a safe anaesthetic for coronary revascularization in patients with unimpaired left ventricular function.

Adult↗
PubMed1983

Selected nutrient intakes of free-living white children ages 6-19 years. The Lipid Research Clinics Program Prevalence Study.

We report energy intake and selected nutrient intakes-protein, fat (total, saturated, and polyunsaturated), carbohydrate (total, starch, and sucrose), and cholesterol-for 1251 white children ages 6-19 years. The data were obtained, by means of a 24-h dietary recall, from children who were randomly selected from the North American populations studied by the Lipid Research Clinics Program. Females (N = 584) consumed about 2000 kcal daily, an intake that remained relatively constant throughout the age groups studied. Males (N = 667) had an energy intake of 2000 kcal/day during childhood that increased to over 3000 kcal/day in adolescence. Energy sources for both sexes were approximately 15% protein, 38% total fat, 15% saturated fat, 6% polyunsaturated fat, 48% total carbohydrate, 19% starch, and 11% sucrose; cholesterol intake averaged about 145 mg/1000 kcal. For both sexes, fat intake increased with age. Compared to females, males ingested greater amounts of cholesterol and total and saturated fat.

Adolescent↗